1. Field of the Invention
The present invention relates to a device for sensing a vibration displacement generated by a first material located inside a second material, which has an acoustic impedance different from that of the first material, by means of using a sensing assembly composed of a piezoelectric substrate, an input interdigital transducer, a first- and a second output interdigital transducers.
2. Description of the Prior Art
There are two types, that is, a touch-type and an untouch-type, of conventional devices for sensing a vibration displacement. For example, an electric micrometer for measuring a minute displacement, a linear scale for a large displacement, and a rotary encoder for a rotation displacement belong to the touch-type of device. The electric micrometer and the linear scale is used as, for example, a reference for measuring the length of a material. The rotary encoder is used for controlling a rotation velocity or a rotation frequency of a rotatory material. The touch-type of device has some problems on measurement accuracy, response time, difficulty in use, durability and manufacturing. On the other hand, for example, a laser-type sensor and an electroacoustic-type sensor belong to the untouch-type of device. The laser-type sensor including a semiconductor position-sensing device is mainly used for measuring a vibration displacement along the direction vertical to the laser beam applied to a material. The laser-type sensor has a defect that the longer the length of the laser beam, the lower the measurement accuracy because of flickering of the laser beam itself. In addition, the use of the laser-type sensor is impossible for the measurement in opaque media. The electroacoustic-type sensor is used for measuring the vibration displacement in a material near a terminal of a pipe. The electroacoustic-type sensor is easy to be affected by a change in circumstances, and has some problems on measurement accuracy, and so on.
An object of the present invention is to provide a vibration displacement sensing device capable of sensing a vibration displacement generated by a first material located inside a second material, which has an acoustic impedance different from that of the first material, with a high sensitivity.
Another object of the present invention is to provide a vibration displacement sensing device capable of operating at a high frequency.
Another object of the present invention is to provide a vibration displacement sensing device capable of transducing a vibration displacement to an electric signal.
Another object of the present invention is to provide a vibration displacement sensing device excellent in measurement accuracy, response time, durability, manufacturing.
Another object of the present invention is to provide a vibration displacement sensing device which is not affected by a change in circumstances, for example, a change in temperature.
A still other object of the present invention is to provide a vibration displacement sensing device easy in use and having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided a vibration displacement sensing device comprising a piezoelectric substrate having two end surfaces an input interdigital transducer, a first output interdigital transducer, a second output interdigital transducer, and a signal analyzer. All the input-, the first output-, and the second output interdigital transducers are formed on one end surface of the piezoelectric substrate.
If an input electric signal is applied to the input interdigital transducer, an elastic wave is excited in the piezoelectric substrate. A leaky component of the elastic wave is radiated effectively in the form of a longitudinal wave toward a first material located inside a second material which is in contact with the other end surface of the piezoelectric substrate and has an acoustic impedance different from that of the first material. The longitudinal wave is reflected by the first material. A reflected longitudinal wave is detected at the first output interdigital transducer as a first delayed electric signal. A non-leaky component of the elastic wave is detected at the second output interdigital transducer as a second delayed electric signal. A vibration displacement caused by the first material is sensed by the signal analyzer from a difference between the first- and second delayed electric signals.
According to another aspect of the present invention there is provided a cellular tissue in contact with the other end surface of the piezoelectric substrate, and a blood vessel located in the cellular tissue. In this case, the blood vessel reflects the longitudinal wave.
According to another aspect of the present invention there is provided an amplifier connected between the input interdigital transducer and the second output interdigital transducer. A part of the second delayed electric signal is amplified via the amplifier, and is fed back as the input electric signal again. Thus, the input interdigital transducer, the second output interdigital transducer and the amplifier form a self-oscillation type of delay-line oscillator.
According to another aspect of the present invention there is provided an amplifier connected between the input interdigital transducer and the first output interdigital transducer. A part of the first delayed electric signal is amplified via the amplifier, and is fed back as the input electric signal again. Thus, the input interdigital transducer, the first output interdigital transducer and the amplifier form a self-oscillation type of delay-line oscillator.
According to another aspect of the present invention there is provided a signal analyzer comprising a phase comparator, which compares an acoustic phase delay of the first delayed electric signal with that of the second delayed electric signal. Thus, a vibration displacement caused by the first material is sensed by the signal analyzer in terms of a phase difference between the firsthand second delayed electric signals.
According to another aspect of the present invention there are provided an input-, a first output-, and a second output interdigital transducers having an arch-shape, respectively, and arranged to have one concentric center.
According to other aspect of the present invention there is provided a piezoelectric substrate made of a piezoelectric ceramic thin plate, of which the polarization axis is parallel to the thickness direction thereof.
According to a further aspect of the present invention there is provided a piezoelectric polymer thin plate.